The cruel firebug who burned an elderly Brooklyn woman to death in her apartment building’s elevator pleaded guilty to murder and arson today — and will likely spend the rest of his life behind bars.

Under his plea deal Jerome Isaac, 48, will be locked away for 25 years to life on a first-degree murder charge and another 25 years on an arson charge.

“He will never again be a free man,” said assistant district attorney Mark Hale. “We don’t have to worry about Mr. Isaac anymore.”

Isaac had previously confessed to cornering Dolores Gillespie, 73, in the elevator, spraying her with gasoline, setting her ablaze with a barbeque lighter, and then throwing a Molotov cocktail on the church-going woman as her screams echoed through her Prospect Heights building.

In order to plead guilty Isaac had to describe his crime to Brooklyn Supreme Court Justice Vincent Del Giudice.

“How did you set fire to Mrs. Gillespie?” asked Del Giudice.

“I sprayed her with gas,” said Isaac, whose face showed no emotion and little sign of the terrible burns he sustained in the attack.

“And you lit the gas?” Del Giudice pressed.

“Yes,” Isaac said.

Issac was also ordered to pay $127,228.75 in restitution for the damage caused by the December arson murder. He will be back in court Nov. 30 for the official sentencing.